That's no joke about being spaghetti code. 16K bytes of program running in a 2K memory space by bank switching the EPROM with 256 bytes of code in a non bank switched location. Plus a bank switched RAM. The darn thing even runs code in a 16 byte memory space reserved for card I/O.

I've read csa2programmer newsgroup for a few years,
including Paul Santa Maria's posts.. I never knew he
was involved in commercial Apple II products. The above
link says he worked for ProDev inc, the company that
manufactured the DDT card